Thermostatic expansion valves are used to control or meter the flow of refrigerant to an evaporator in an air conditioning system, to provide a refrigerant flow rate into the evaporator that approximately matches the refrigerant flow exiting the evaporator. The thermostatic expansion valve typically permits fluid flow from the inlet to the outlet during normal operation of the air conditioning system, where the fluid at the inlet is typically at a higher pressure than the fluid at the outlet. Where the air conditioning system also functions as a heat pump in which refrigerant flow is reversed, a check valve is typically plumbed in parallel to the expansion valve to permit refrigerant flowing in a direction opposite that of the typical expansion valve to bypass the valve.